1. Field of the Invention:
This invention relates to coil spring dampers and, more particularly, to coil spring dampers for valve assemblies in internal combustion engines.
2. Disclosure Information:
It has long been known that a coil spring is well suited for providing a biasing force for a valve assembly that must undergo repetitive reciprocal motion. Engine tappet valves are usually biased to a closed position by coil springs. The valves are repetitively opened by mechanical actuators against the closing bias of the spring. When engines run at high speed, the tappet valves repetitively open and close at high frequencies. At these high frequencies, it is known that coil springs may resonate and start to vibrate and oscillate in an undesired fashion which may interfere with its desired functions.
Various devices and techniques to damp the resonance of the coil spring are known. A metal cylinder positioned within the inner diameter of the coil spring such that the inside portion of the coils frictionally slide against the cylinder damps the resonating motion of the spring. However, the cylinder by being on the inside of the coil spring rubs against the high stress areas of the coils. It is desirous to eliminate the frictional engagement of a damper with the high stress area; i.e., the inner diameter portion of the coil spring.
It is known to use a second coil spring to damp motion of the main coil spring. The second spring is wrapped on the inside or outside of the coil. This secondary spring is disclosed in U.S. Pat. No. 1,928,678 issued to Sjolander on Oct. 3, 1933. The disadvantage of the secondary spring is that it adds an additional load which must be overcome to open the valve head. At low speeds, the increased loads may deteriorate fuel economy.
U.S. Pat. No. 2,005,089 issued to Krebs on June 18, 1935 discloses an elastomeric tube placed about the coil spring. The tube compresses as the coil spring compresses to act as a secondary spring which must be overcome in order for the valve head to move to its open position.
It is desired to have a damper which does not appreciably increase the load needed to compress the spring and does not engage high stress areas of the coil spring. It is also desirable to have a damper which can be incorporated in existing engines.